This invention is generally directed to developer compositions, and more specifically, the present invention relates to developer compositions wherein the toner resin particles are comprised of specific styrene butadienes. More specifically, in one embodiment of the present invention there are provided developer compositions formulated by admixing toner compositions and carrier components, and wherein the toner compositions contain therein as resin particles suspension polymerized styrene butadiene as illustrated in U.S. Pat. No. 4,558,108, the disclosure of which is totally incorporated herein by reference. Of further importance with respect to the invention of the present application is the selection of carrier particles prepared by a dry coating process wherein a mixture of certain polymers is applied to the carrier enabling insulating particles with relatively constant conductivity parameters; and also wherein the triboelectric charge on the carrier can vary significantly depending on the coatings selected. The aforementioned carrier particles are illustrated in U.S. Ser. No. 793,042, the disclosure of which is totally incorporated herein by reference. Developer compositions of the present invention possess at low (about 20 percent) and high (about 80 percent) relative humidities stable triboelectric charging values for extended time periods exceeding, for example, two million imaging cycles; rapid admix characteristics; excellent blocking and fusing properties; and excellent aging characteristics. The toner and developer compositions of the present invention are particularly useful in electrophotographic printing and imaging systems, especially xerographic imaging process. Furthermore, in the aforementioned imaging processes the triboelectric charge on the carrier particles can be preselected independent of the conductivity depending, for example, on the polymer composition applied to the carrier cores.
The electrophotographic process, and particularly the xerographic process, is well known. This process involves the formation of an electrostatic latent image on a photoreceptor, followed by development, and subsequent transfer of the image to a suitable substrate. Numerous different types of xerographic imaging processes are known wherein, for example, insulative developer particles or conductive toner compositions are selected depending on the development systems used. Moreover, of importance with respect to the aforementioned developer compositions are appropriate triboelectric changing values associated therewith, as it is these values that enable continued constant developed images of high quality and excellent resolution; and admixing characteristics. Thus, toner and developer compositions are known, wherein there are selected as the toner resin styrene acrylates, styrene methacrylates, and certain styrene butadienes including those available as Pliolites. Other resins have also been selected for incorporation into toner compositions inclusive of the polyesters as illustrated in U.S. Pat. No. 3,590,000. Moreover, it is known that single component magnetic toners can be formulated with styrene butadiene resins, particularly those resins available as Pliolite. In addition, positively charged toner compositions containing various resins, inclusive of certain styrene butadienes and charge enhancing additives, are known. For example, there are described in U.S. Pat. No. 4,560,635, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions with distearyl dimethyl ammonium methylsulfate charge enhancing additives. This patent also illustrates the utilization of suspension polymerized styrene butadiene for incorporation into toner compositions, reference working Example IX.
In addition, a number of different carrier particles have been illustrated in the prior art, reference for example the U.S. Pat. No. 3,590,000 mentioned herein; and U.S. Pat. No. 4,233,387, wherein coated carrier components for developer mixtures which are comprised of finely divided toner particles clinging to the surface of the carrier particles are recited. Specifically, there are disclosed in the '387 patent coated carrier particles obtained by mixing carrier core particles of an average diameter of from about 30 microns to about 1,000 microns with from about 0.05 percent to about 3.0 percent by weight, based on the weight of the coated carrier particles, of thermoplastic resin particles. More specifically, there are illustrated in the '387 patent processes for the preparation of carrier particles by a powder coating process; and wherein the carrier particles consist of a core with a coating thereover comprised of polymers. More specifically, the carrier particles selected can be prepared by mixing low density porous magnetic, or magnetically attractable metal core carrier particles with from, for example, between about 0.05 percent and about 3 percent by weight, based on the weight of the coated carrier particle of polymers until adherence thereof to the carrier core by mechanical impaction or electrostatic attraction; heating the mixture of carrier core particles and polymers to a temperature of between from about 200.degree. F. to about 550.degree. F. for a period of from about 10 minutes to about 60 minutes enabling the polymers to melt and fuse to the carrier core particles; cooling the coated carrier particles; and thereafter classifying the obtained carrier particles to a desired particle size. Also, in a specific embodiment of the aforementioned copending application U.S. Ser. No. 793,042, there are disclosed carrier particles comprised of a core with a coating thereover comprised of a mixture of a first dry polymer component and a second dry polymer component not in close proximity to the first polymer in the triboelectric series. Therefore, the aforementioned carrier compositions can be comprised of known core materials including iron with a dry polymer coating mixture thereover. Subsequently, developer compositions can be generated by admixing the aforementioned carrier particles with a toner composition comprised of resin particles and pigment particles.
Other patents of interest include U.S. Pat. No. 3,939,086, which teaches steel carrier beads with polyethylene coatings, see column 6; U.S. Pat. Nos. 3,533,835; 3,658,500; 3,798,167; 3,918,968; 3,922,382; 4,238,558; 4,310,611; 4,397,935; and 4,434,220. Moreover, there are illustrated in U.S. Pat. No. 4,469,770, toner and developer compositions wherein there is incorporated into the toner styrene butadiene resins prepared by emulsion polymerization processes.
Additionally, in copending U.S. applicaton Ser. No. 751,922, the disclosure of which is totally incorporated herein by reference, entitled Developer Compositions With Specific Carrier Particles, developers containing toners with styrene butadiene copolymers, pigment particles inclusive of magnetites, charge control additives, and carrier particles containing a core with a coating thereover of vinyl copolymers, or homopolymers, such as vinyl chloride/vinyl acetate are illustrated. The aforementioned carrier particles can be prepared by solution coating processes.
With further respect to carrier particles, recent efforts have focused on the attainment of coatings for these particles for the purpose of improving development quality; and also to permit particles that can be recycled, and that do not adversely effect the imaging member in any substantial manner. Many of the present commercial coatings can deteriorate rapidly, especially when selected for a continuous xerographic process where the entire coating may separate from the carrier core in the form of chips or flakes; and fail upon impact, or abrasive contact with machine parts and other carrier particles. These flakes or chips, which cannot generally be reclaimed from the developer mixture, have an adverse effect on the triboelectric charging characteristics of the carrier particles thereby providing images with lower resolution in comparison to those compositions wherein the carrier coatings are retained on the surface of the core substrate. Further, another problem encountered with some prior art carrier coatings resides in fluctuating triboelectric charging characteristics, particularly with changes in relative humidity. The aforementioned modification in triboelectric charging characteristics provides developed images of lower quality, and with background deposits. With the developer compositions of the present invention, these disadvantages are alleviated.
Furthermore, with reference to the prior art, carriers obtained by applying insulating resinous coatings to porous metallic carrier cores using solution coating techniques are undesirable from many viewpoints. For example, the coating material will usually reside in the pores of the carrier cores, rather than at the surfaces thereof; and therefore is not available for triboelectric charging when the coated carrier particles are mixed with finely divided toner particles. Attempts to resolve this problem by increasing the carrier coating weights, for example, to as much as 3 percent or greater to provide an effective triboelectric coating to the carrier particles necessarily involves handling excessive quantities of solvents, and further usually these processes result in low product yields. Also, solution coated carrier particles when combined and mixed with finely divided toner particles provide in some instances triboelectric charging values which are too low for many uses. The powder coating process selected for the carrier components of the present invention overcomes these disadvantages, and further enables developer mixtures that are capable of generating high and useful triboelectric charging values with finely divided toner particles; and also wherein the carrier particles are of substantially constant conductivity. Further, when resin coated carrier particles are prepared by the powder coating process of the present invention, the majority of the coating materials are fused to the carrier surface thereby reducing the number of toner impaction sites on the carrier material. Additionally, there can be achieved with the carrier particles of the present invention, independent of one another, desirable triboelectric charging characteristics and conductivity values; that is, for example, the triboelectric charging parameter is not dependent on the carrier coating weight as is believed to be the situation with the process of U.S. Pat. No. 4,233,387 wherein an increase in coating weight on the carrier particles may function to also permit an increase in the triboelectric charging characteristics. Specifically, therefore, with the carrier compositions and process of the present invention there can be formulated developers with selected triboelectric charging characteristics and/or conductivity values in a number of different combinations.
Thus, for example, there can be formulated in accordance with the invention of the present application developers with breakdown voltages of from about 1,000 to in excess of about 2,000 as determined in a magnetic brush conducting cell. In this device, the carrier composition or developer composition can be placed on a 1.5 inch diameter magnetic roll, followed by applying a voltage across the composition, and measuring with a probe the amount of current which passes through the carrier composition or the developer composition to a measurement electrode for a specific applied voltage V. The measurement electrode surrounded by a grounded guard plate has a surface area of 3.0 cm.sup.2, and the developer roll to electrode spacing is usually about 2.54 millimeters. The breakdown potential is that potential at which these components begin to conduct large electrical currents, that is currents approaching 0.1 milliamps. Also, the developer compositions of the present invention possess triboelectric charging values of from about 10 to 35 microcoulombs per gram on the carrier particles as determined by the known Faraday Cage technique. Thus, the developers of the present invention can be formulated with constant conductivity values with different triboelectric charging characteristics by, for example, maintaining the same coating weight on the carrier particles and changing the polymer coating ratios. Similarly, there can be formulated developer compositions wherein constant triboelectric charging values are achieved, and the conductivities are altered by retaining the polymer ratio coating constant and modifying the coating weight for the carrier particles. Also, with the present invention there is provided toner and developer compositions with other improved characteristics, including superior aging properties. Thus, there is a need for developer compositions with stable charging characteristics. There is also a need for positively charged toner compositions with many of the advantages indicated herein, and wherein there is selected specific styrene butadiene resins. In addition, there is a need for positively charged toner compositions, especially those with magnetites therein which possess excellent blocking properties, acceptable fusing temperature latitudes, and superior charging properties. There is also a need for toner and developer compositions possessing excellent admix charging times of, for example, less than 15 seconds; and wherein the aforementioned compositions are insensitive to relative humidities of from about 20 to about 80 percent. Furthermore, there is a need for toner and developer compositions that will enable the generation of excellent solid areas, substantially no background deposits, and full gray scale reproduction of half tone images.